In the U.S., prostate cancer is the most common male cancer and the second leading cause of cancer deaths in men. The long-term objective of this proposal is to develop small RNA-based therapeutic strategies for prostate cancer. Small double-stranded RNA (dsRNA) has been widely used as small interfering RNA (siRNA) to knockdown gene expression by targeting mRNA sequences, a phenomenon known as RNA interference (RNAi). Recently we and others identified a new mechanism of small RNA-mediated gene regulation in which dsRNA molecules targeting gene promoter regions induce sequence-specific transcriptional gene activation, a phenomenon termed "RNA-induced gene activation" (RNAa) and the dsRNA molecules "small activating RNAs" (saRNAs). We demonstrated that RNAa is potent in gene activation and its effects are long-lasting, suggesting a promising therapeutic role for RNAa. We hypothesize that saRNA molecules have anti-tumor activity in vitro and in vivo via targeted activation of tumor suppressor genes (TSGs) in prostate cancer. This hypothesis will be tested in two specific aims. Specific Aim #1. Identify functional saRNAs for TSG activation and evaluate their anti-growth effects in cultured human prostate cancer cells. Genes to be targeted for activation include (1) negative cell cycle regulators such as p16, p21, p27 and p53, (2) genes that inhibit tumor cell invasion and metastasis including E-cadherin, KAI1 and CD44, and (3) pro-apoptosis genes including Par-4 and caspase-7. Candidate saRNAs targeting gene promoters will be transfected into human prostate cancer cell lines LNCaP and PC3, and the expression of targeted genes will then be evaluated at both mRNA and protein levels. Functional saRNAs will be further assessed for their anti-growth activity and effects on cell cycle distribution, apoptosis, clonogenicity, invasion and migration. Specific Aim #2. Evaluate saRNA's anti-tumor activity in xenograft human prostate tumor models. Xenograft prostate tumors will be established in athymic mice using human prostate cancer PC-3 cells. Mice with established tumors will be treated with functional saRNAs by intratumoral injections. Tumor growth in saRNA-treated mice will be compared with mice treated with control saRNAs. These studies constitute a logical progression of our previous work. Successful completion of this proposal will provide rationale for further clinical trials of RNAa. In the U.S., prostate cancer is the most common male cancer and the second leading cause of cancer deaths in men. There is an urgent need to develop novel therapeutic strategies for prostate cancer. This project will investigate the therapeutic use of a newly identified method of gene therapy using small RNA molecules.